Etching system and etching method

ABSTRACT

An etching system for subjecting a single film to be etched to etching comprised of a plurality of etching steps applying respective different recipes. The etching system comprises a recipe generating means which fixes the recipe to be applied to the final etching step affecting an underlying film making contact with the film to be etched, of the etching steps, to a preset recipe and which generates a recipe to be applied to the residual etching step on the basis of the results of processing, and etching processing is conducted according to the recipes generated by the recipe generating means.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an etching system and an etching method, and particularly to an etching system and an etching method that can suppress influences of disturbances.

[0002] An etching system using a plasma is so operated, for example, that an etching gas is introduced into a vacuum process chamber, a plasma discharge is caused under a reduced pressure, radicals or ions generated in the plasma are led to the surface of a wafer which is the workpiece to be processed, and a reaction is caused at the wafer surface, thereby performing etching of the wafer surface. The etching system for performing such a processing (dry processing) is operated to perform the etching based on preset production conditions (gas flow rate, gas pressure, electric power supplied, etching time, etc.) called “recipe”.

[0003] The recipe is generally maintained constant during a production step (an etching step for a single film to be etched) consisting of a specified same process for semiconductor devices, excluding a production process of a photomask or the like in which, for example, one process is divided into several steps and production conditions are modified on the basis of each step.

[0004] However, even if a fixed etching using a fixed recipe is conducted, various disturbances such as secular change of the system make it difficult to constantly obtain fixed performance.

[0005] As a method of restraining the disturbances, for example, Japanese Patent Application No. 2001-198830 discloses a technique in which the processed results are monitored and information is fed back to the recipe based on the monitored results.

[0006] In the case of monitoring the processed results of a specimen such as a semiconductor wafer and feeding back the monitored results to the recipe, the elements constituting the recipe include a number of parameters such as gas flow rate, pressure, electric power supplied, and etching time. In order to specify an optimum parameter for control from among these parameters and build up a control model by use of the specified parameter, it is necessary to perform a number of experiments and simulations with enormous labor and time.

[0007] In addition, even if the optimum control model is built up, unexpected side effects may be generated. For example, in a gate etching step for forming a gate electrode of an FET (Field Effect Transistor), etching which does not impair a thin gate insulation film present beneath the film to be etched is required for not producing influences on the device performance. However, in the case where the characteristics of the system are varied in the direction of worsening the selectivity ratio between the film to be etched and the gate insulation film, as a result of the feedback of the monitored results to the recipe, the gate insulation film is also processed, and the gate insulation film is damaged.

[0008] That is, even where it is estimated to restrain various disturbances by a feedback control, realization of this in an actual production process requires enormous labor and time, and, further, there is still fear of unexpected side effects.

SUMMARY OF THE INVENTION

[0009] The present invention has been made in view of the forgoing. Accordingly, it is an object of the present invention to provide an etching system and an etching method which can alleviate the fear of unexpected side effects, particularly when a feedback control is performed, and can build up a control model without using enormous labor and time.

[0010] According to an aspect of the present invention, there is provided an etching system for subjecting a single film to be etched to etching comprised of a plurality of etching steps applying respective different recipes, wherein the etching system comprises a recipe generating means which fixes a recipe to be applied to the last etching step affecting an underlying film making contact with the film to be etched, of the etching steps, to a preset recipe and which generates recipes to be applied to the residual etching steps on the basis of processed results, and the etching is conducted according to the recipes generated by the recipe generating means.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other objects and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying drawings in which:

[0012]FIG. 1 is an illustration of an etching system according to one embodiment of the present invention;

[0013]FIG. 2 illustrates a gate electrode forming process;

[0014]FIG. 3 is an illustration of the processing conducted by the etching system;

[0015]FIG. 4 is a diagram showing CD value control characteristic relative to oxygen flow rate;

[0016]FIG. 5 illustrates a recipe adjustment method;

[0017]FIG. 6 illustrates a control mechanism for CD value at the time of varying the oxygen flow rate;

[0018]FIG. 7 illustrates a modified example of the etching system;

[0019]FIG. 8 is a flow diagram illustrating a control flow for CD value;

[0020]FIG. 9 is a flow diagram illustrating another example of the control flow for CD value;

[0021]FIG. 10 illustrates determinative factors for gate length; and

[0022]FIG. 11 illustrates a method of using a film thickness monitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Preferred embodiments of the present invention will be described below referring to the accompanying drawings. FIG. 1 is an illustration of an etching system according to one embodiment of the present invention. In the figure, a main body 300 of the etching system comprises a process chamber (process vessel) 201, a gas supply means 202 for supplying a process gas into the process chamber, and a gas exhaust means 203 for exhausting the process gas and controlling the pressure in the process chamber. Further, a specimen table 205 for supporting a specimen 204 as an object of processing is provided in the process chamber 201, and a plasma generating means 206 for generating a plasma is provided in the process chamber.

[0024] The plasma generating means comprises an electromagnetic wave supply means 301 for supplying by transmitting an electromagnetic wave into the process chamber 201, and solenoid coils 302, 303 for generating a magnetic field in the process chamber 201. A high frequency voltage is applied to the specimen table 205 from a high frequency power source 304 so that a reaction product produced by the plasma generated is led toward the specimen.

[0025] This dry etching system is provided with a system condition detecting means 208. The system condition detecting means 208 comprises, for example, a monitor for detecting the flow rate of the gas supplied from the gas supply means 202, detectors for detecting the current and voltage in a feeder for supplying electric power for generation of plasma, a detector for detecting the phase difference between the current and the voltage, detectors for detecting a progressive wave and a reflected wave of the high frequency electric power supplied for generation of plasma, and an impedance monitor.

[0026] The system condition detecting means 208 is provided with an analyzer for detecting and analyzing the light emitted from the plasma generated by the plasma generating means 206 in the process chamber 201. The system condition detecting means 208 is desirably a detector for outputting a multiplicity of signals such as a spectroscope for outputting an emission spectrum resolved on a wavelength basis, but may be a detector for picking up light with a single wavelength such as a monochromator. The emission spectrum as an output from the spectroscope is a signal indicating the light intensity on a wavelength basis. In addition, the system condition detecting means 208 may be a general plasma state monitor such as a quadrupole mass spectroscopy (QMS) apparatus for outputting a mass spectrum of the substances in the plasma.

[0027] Further, in this embodiment, a controller 209 for receiving the output from the system condition detecting means 208 and controlling the operation of the system is provided. The controller 209, for example, controls the supply and interruption of the electric power supplied to the plasma generating means 206 comprising a magnetron or the like for generating an electromagnetic wave or a magnetic field for generating a plasma, or controls the electric power supplied. Besides, it is also possible to control the output of plasma generated by use of other means. For example, the system condition detecting means 208 may detect the reaction conditions such as variations (increase and decrease) of a specified reaction quantity relevant to the processing, reaction rate, intensity of plasma, etc. based on detection data obtained by detecting light with a predetermined wavelength generated during the processing of the specimen by use of the plasma, and instructions for the generation and stoppage of the plasma or for the starting and stoppage of the system may be issued, whereby the operation of the system can be controlled.

[0028] In addition, the controller 209 can control the operation of the etching system by receiving an output from a detector 210 provided separately from or integrally with the etching system. The detector 210, for example, is generally a CD-SEM (scanning electron microscope) for measuring the processed shape upon etching, but may be a processed shape measuring means of the optical type called scatrometry which utilizes scattering of light.

[0029]FIG. 2 is a schematic illustration, on a process step basis, of a gate electrode forming process in the case of a semiconductor device as an object of processing by the etching system according to the present embodiment. In the figure, numeral 110 denotes a wafer comprising a silicon substrate 111, a gate insulation film 112, and a polysilicon film 113 as a single film to be etched. The wafer 110 is provided with a mask 114, and a natural oxide film 115 is formed on the surface of the wafer.

[0030] The etching will be described referring to FIG. 2. First, in Step 1, the wafer 110 provided with the mask 104 is prepared. Since the natural oxide film 115 is formed on the surface of the polysilicon 113 in areas not covered with the mask 104, removal (breakthrough) of the natural oxide film 115 is conducted in Step 2. In Step 3, an etching with a good shape is conducted by adopting such a recipe that a high etching rate can be maintained (main etching 1). In Step 4, such a processing as not to affect the gate insulation film 112 is conducted by adopting such a recipe that a selectivity ratio between the polysilicon 113 and the gate insulation film 112 can be maintained (main etching 2). In Step 5, the residue of the film to be etched is removed by etching (over-etching).

[0031] In the above-mentioned etching, the “main etching” means the step of etching the film to be etched, excluding the step of removing the substance on the surface of the film to be etched such as the natural oxide film (breakthrough) and the step of removing the residue of the film to be etched (over-etching).

[0032] Incidentally, in order to contrive a higher device speed and a lower power consumption, the gate length 200 shown in FIG. 2 has been decreasing year by year. The gate length of the device is an important dimension for determining the device characteristics, and, therefore, it is called CD (Critical Dimension) value. As the gate length has decreased, the variations of the gate length allowed in gate etching has also decreased to the order of several nm, and there is an increasing need for an etching process by which the device can be produced with a stable gate length. In addition, with the miniaturization of gate length, the gate insulation film has been becoming more and more thinner. For example, where the gate length is 100 nm, the thickness of the gate insulation film is about 2 nm. For such a gate insulation film, etching which does not damage the gate insulation film is required so as to obviate deterioration in insulation characteristics of the gate insulation film.

[0033] In general, a dry etching system determines production conditions (gas flow rate, gas pressure, electric power supplied, etching time, etc.) called recipe prior to the production (mass-production) so as to fulfill the dimensions and shape required of the work (specimen), namely, the object of processing. As has been described above, it is a usual practice to maintain the recipe constant during the production (mass-production), excluding the process for producing a photomask. However, even if the etching is conducted by use of a fixed recipe as above-mentioned, various disturbances such as secular change of the systems make it difficult to constantly obtain fixed results of etching.

[0034]FIG. 3 illustrates the processing conducted by use of the etching system according to the present embodiment. In the figure, numeral 1 denotes a plasma etching process chamber for generating a plasma 1 c therein, and symbol 1 b denotes a wafer as the workpiece to be processed which is mounted on a wafer stage 1 a in the process chamber 1. Numeral 2 denotes sensors for monitoring the process quantities during processing such as the flow rate and pressure of the gas supplied into the apparatus, or electric power supplied, and these sensors are generally standard equipment of the plasma etching system. Numeral 3 denotes additional sensors, for example, an OES (Optical Emission Spectroscopy) sensor for monitoring the spectrum of plasma light, a QMS (Quadrupole Mass Spectrometry) apparatus for analyzing the masses in the plasma, etc. Numeral 4 denotes actuators for controlling the etching system according to the recipe 5. Numeral 6 denotes a control model unit for calculating the recipe 5 based on the results of processing obtained from an inspection apparatus 7, and the recipe 5 can be modified on a wafer processing basis or during the processing.

[0035] The inspection apparatus 7 is ordinarily a CD SEM as a general choice, but may be a scatrometry (light scattering type shape measuring means) which is disposed separately from the etching system and measures the dimensions and shape through utilizing scattering of light. This apparatus may be integrally incorporated into the etching processing apparatus.

[0036] The wafers 8 supplied from the preceding step are supplied into the plasma etching process chamber 1. The wafers thus supplied are processed on the basis of lot (a plurality of wafers) to be etched wafers 9. The wafers 9 are supplied to the inspection apparatus 7 such as CD-SEM, for inspection of the results of etching (processing). The wafers 10 thus inspected are fed to the subsequent step.

[0037] The result (CD value) inspected by the inspection apparatus 7 is treated to calculate the deviation thereof from a target value, and the calculation result is outputted to the control model unit 6. In the control model unit 6, a recipe for the wafers for the next processing which uses roughly the same degree of process is calculated based on a CD value control model 11 previously built up by use of experiments or simulations. According to the recipe thus calculated, the next etching is started.

[0038] A cause of anxiety in such a feedback control is the side effects of the control mentioned above. More specifically, in the gate etching step, etching such as not to damage the thin gate insulation film beneath the film to be etched is required. However, where control including an adjustment of the recipe as mentioned above is performed, a variation in the direction of worsening the selectivity ratio between the film to be etched and the gate insulation film may occur; if this variation occurs, there is generated a side effect that the gate insulation film is also processed.

[0039]FIG. 4 is a diagram showing the CD value control characteristic relative to oxygen (O₂) flow rate in the above-mentioned main etching 1. As shown in the diagram, there is a linear control characteristic, from which it is seen that the oxygen (O₂) flow rate in the main etching 1 is an effective control parameter for the control of CD value. In addition, in the main etching 1, the gate insulation film is not exposed during the etching, and therefore, it is unnecessary to take into account the side effect on the gate insulation film. While the control factor and the result are in a linear relationship in the example shown in FIG. 4, the present invention can be applied also to the case where the relationship is not linear.

[0040] In other words, in an etching control intended to constantly obtain fixed results in the possible presence of various disturbances, control such as not to damage the gate insulation film is conducted as follows. The recipes for the steps in which the gate insulation film might be exposed such as the main etching 2 and the over-etching are fixed, at least one of the steps in which the gate insulation film would not (might not) be exposed such as the breakthrough and the main etching 1 is selected as an object, at least one parameter in the object step is set to be a variable parameter, and a feedback control (recipe adjustment) is conducted by use of the variable parameter. For example, in the case where oxygen (O₂) is selected as a control parameter as above-mentioned, the recipes other than oxygen (O₂) in the main etching 1 (ME1) are fixed and only the flow rate of oxygen (O₂) is set to be variable, as shown in FIG. 5.

[0041]FIG. 6 illustrates the mechanism of control of the CD value when the flow rate of oxygen (O₂) is varied in the main etching 1. When the flow rate of oxygen (O₂) in the main etching 1 (etching of an upper layer portion of the film to be etched; ME1) is increased, build-up of the material to be etched onto side walls is increased to form a side wall protective film. Therefore, the gate size (CD value) obtained after completion of the main etching is greater by about several nm than that before the increase in the flow rate of oxygen (O₂). Incidentally, the CD value can be reduced by decreasing the flow rate of oxygen (O₂) in reverse to the above.

[0042] Next, in the main etching 2 (etching of a lower layer portion of the film to be etched; ME2), the side wall protective film formed upon completion of the main etching 1 functions. Therefore, the initial size and shape in the main etching 2 succeed to the size and shape upon completion of the main etching 1, resulting in that the CD value is greater by several nm.

[0043] The important part (CD value) as the gate length which affects the device characteristics is the size of the lowermost portion (skirt portion) of the polysilicon layer etched; therefore, it is important to stably process the size of that portion.

[0044] Here, it is important that the flow rate of oxygen (O₂) as a variable parameter cannot be varied limitlessly. For example, when the CD value upon the preceding etching is smaller than the target value by about 10 nm, the required flow rate of oxygen (O₂) calculated based on the CD control characteristic versus oxygen (O₂) flow rate shown in FIG. 4 exceeds a preset control range of the variable parameter (over-control). In this case, the flow rate of oxygen (O₂) cannot be increased according to the calculation result, because an excessive increase in the flow rate of oxygen (O₂) may generate another side effect which matters on the basis of device performance. Therefore, in the case of using the flow rate of oxygen (O₂) as a variable parameter, it is necessary to preliminarily set upper and lower limits of the flow rate, and to output an alarm, stop the etching or set the flow rate to the upper or lower limit thereof when the flow rate of oxygen (O₂) obtained upon calculation of the recipe exceeds the upper or lower limit thereof.

[0045] While oxygen (O₂) has been selected as a variable parameter in the present embodiment, other factors may also be adopted as the variable parameter; for example, etching time, RF or pulse biased power applied to the substrate to be processed, etching gas flow rate ratio (Cl₂/(HBr+Cl₂)), and flow rate of an additive gas such as N₂ may be adopted. Where the etching time is selected as the variable parameter, a film thickness monitor for monitoring the film thickness during processing may be used jointly, whereby a difference in initial film thickness can be accommodated. In the etching with such high accuracy as to be an object of the present invention, it is desirable to devise a way to maintain the processed film thicknesses in all steps at set points by use of a film thickness monitor. Also in the cases of controlling these variable parameters, it is important to preliminarily set variable ranges of the variable parameters, for coping with over-control.

[0046]FIG. 7 illustrates a modified example of the etching system according to the present embodiment. In the figure, the same portions as those shown in FIG. 3 are denoted by the same symbols, and the description thereof will be omitted. It is known that the results of an etching are in intimate relationship with the environments in the process chamber during the etching. Therefore, by monitoring the conditions in the process chamber by sensors 2 and additional sensors 3, the processed conditions can be estimated on the basis of the monitored conditions by a processed condition estimating unit 20. For estimation of the processed conditions, a prediction model 21 built up based on the results of experiments or simulations preliminarily conducted is used.

[0047] After built up, the model is stored in the processed result estimating unit 20, and is corrected on the basis of measured values outputted from an inspection apparatus 7 for inspecting the results of the etching. Thus, model accuracy can be enhanced.

[0048] A control model unit 6 adjusts a recipe for the same kind or roughly the same kind of wafers to be processed next, based on the deviation between the processed result estimated as above mentioned and a target value of processed size of the process. In this case, the parameters to be adjusted are limited to the parameters in the etching steps which do not affect the gate insulation film. In the control model 6, a control algorithm is preliminarily built up by confirming control characteristics as for example shown in FIG. 4 by experiments or simulations conducted preliminarily.

[0049]FIG. 8 shows an example of control flow for CD value. In this example, the figure shows the control flow for CD value in the case where an OES sensor is used as the additional sensor 3 in the etching processing apparatus shown in FIG. 7. Each of steps will be described below. In Step 1, a natural oxide film formed on the surface of the film to be etched is removed (breakthrough). In a predetermined period in this step, a plasma emission spectrum is collected by use of the OES sensor. In Step 2, the current system conditions are grasped by use of the emission spectrum data, and the results of processing by the current system are predicted. Further, a recipe to be used in Step 4 is modified on the basis of the predicted results.

[0050] Specifically, the spectrum collected is immediately treated by use of multivariate analysis or a specified filter to calculate several indices as representative values of process condition monitors in Step 1. Next, based on the correlation between the preliminarily formed indices and the CD value which is the final processed result, the result of the etching is estimated from the calculated indices. The merit of this method is as follows. In the conventional control method, a specimen is processed, and the deviation of the processed shape from a reference value is measured, whereby it is only possible to stabilize the processing of the subsequent specimens. In this case, time delay relating to control is large, and many specimens are finished without being corrected by the control. Further, in some cases where some variation as to the system occurs during when the control is delayed, the control itself becomes meaningless.

[0051] On the other hand, in the method of FIG. 8, the processed status of the specimen as the object of control is monitored, and a controlled variable is calculated from the monitored status, so that stable control with very high accuracy can be achieved.

[0052] In Step 3, based on the processed result estimated in Step 2, at least one parameter (variable parameter) in a recipe to be used in Step 4 is adjusted so that the result of the etching will coincide with the target value. In this case, when the adjusted parameter exceeds a preset adjustment range for the parameter, the parameter is set to the nearest value in the adjustment range, or the processing is interrupted and some alarm is issued to the user of the etching system. The variable parameter is not limited to the flow rate of oxygen (O₂). That is, etching time, RF or pulse biased power applied to the substrate to be processed, etching gas flow rate ratio (Cl₂/(HBr+Cl₂)) and flow rate of an additive gas such as N₂ may also be adopted as the variable parameter. Where etching time is adopted as the variable parameter, a film thickness monitor for monitoring the film thickness during processing may be used jointly, whereby differences in initial film thickness can be accommodated.

[0053] In Step 4, the film to be etched is etched by use of the recipe calculated in Step 3. In Step 5, the film to be etched is etched until the gate insulation film is exposed, by use of a recipe with a high selectivity ratio relative to the gate insulation film. In Step 6, the residual portion which could not be etched away in Step 5 is etched (over-etching) for finishing by use of a recipe with such a margin as not to damage the gate insulation film. In FIG. 8, it is intended to detect a variation of the processed condition in the processed condition upon the breakthrough; however, the breakthrough step is short in time and is in may cases unstable, so that there are cases where the variation of the processed condition cannot favorably detected.

[0054]FIG. 9 illustrates an example of another control flow for the CD value so as to cope with this problem. First, in Step 10, the natural oxide film formed on the surface of the film to be etched is removed (breakthrough). In Step 11, the film to be etched is etched. In a predetermined period during this step, a plasma emission spectrum is collected by use of an OES sensor. In Step 12, the current state conditions are grasped by use of the emission spectrum data acquired in Step 11, the result of processing under the current system conditions is predicted, and the recipe to be used in Step 14 is modified.

[0055] Specifically, the spectrum thus collected is immediately treated by use of multivariate analysis or a specified filter to calculate several indices as representative values of a process condition monitor in Step 11. Next, based on the correlation between the indices and the CD value as the final processed result which has been preliminarily formed, the result of etching is estimated from the calculated indices.

[0056] In Step 13, based on the processed result estimated in Step 12, at least one parameter (variable parameter) in the recipe to be used in Step 14 is adjusted so that the result of the etching will coincide with a target value. In this case, when the adjusted parameter exceeds a preset adjustment range for the parameter, the adjusted parameter is set at a nearest value in the adjustment range, or the processing is interrupted and some alarm is issued to the user of the etching system.

[0057] The variable parameter is not limited to the flow rate of oxygen (O₂); namely, etching time, RF or pulse biased power applied to the substrate to be processed, etching gas flow rate ratio (Cl₂/(HBr+Cl₂)), and the flow rate of an additive gas such as N₂ may also be adopted as the variable parameter. Where the etching time is adopted as the variable parameter, a film thickness monitor for monitoring the film thickness during processing may be used jointly, whereby differences in initial film thickness can be accommodated. In Step 14, the film to be etched is etched by use of the recipe calculated in Step 13. In Step 15, the film to be etched is etched until the gate insulation film is exposed, by use of a recipe with a high selectivity ratio relative to the gate insulation film. In Step 16, the residual portion which could not be etched away in Step 15 is etched for finishing (overetching) by use of a recipe with such a margin as not to damage the gate insulation film.

[0058]FIG. 10 illustrates determinative factors for gate length in the etching step. In the figure, the processing is sequentially conducted in the order of Process 1, Process 2, and Process 3 of FIG. 10, and the etching according to the present invention is sequentially conducted in the order to Step 1 and Step 2 of Process 3. In the figure showing these processes, numeral 110 denotes a wafer comprising a silicon substrate 111, a gate insulation film 112, and a polysilicon film 113, the wafer 110 is provided with a hard mask material layer 114′ formed of SiO₂ or the like on the surface thereof, and a resist mask 201 is provided on the hard mask material layer 114′.

[0059] Process 1 is a photolithographic step in a process of fabricating a semiconductor, and shows the condition where the resist mask 201 is formed. Process 2 shows mainly a step of forming the hard mask 114 by etching the hard mask material layer 114′ by use of an insulation film etching system, in an etching step in the process of fabricating the semiconductor. The hard mask 114 functions as a mask at the time of etching a gate material 113 consisting of a polysilicon film or the like, and one of the factors which determine the final gate size. The resist mask 201 is removed after completion of this process.

[0060] Process 3 is a process to which the etching according to the present invention is applied. First, in Step 1, the polysilicon film 113 is etched away up to a point before exposure of the gate insulation film 112, under etching conditions with a high etching rate, for example. During this etching, the residual film amount 209 of the polysilicon film 113 to the gate insulation film 112 is monitored by use of a film thickness monitor, whereby the residual film amount can be maintained constant on a wafer basis. Step 2 is a step of etching for finishing (over etching) the residual portion which could not be etched away in Step 1, by use of a recipe with such a margin as not to damage the gate insulation film.

[0061] For example, in Process 3 for processing the film to be etched in a plurality of steps, the mask size 210 of the hard mask 114 is varied due to process variations inherent in Process 1 or Process 2. Where the mask size 210 is formed to be greater in the preceding process, it may be contemplated to reduce the mask size 210 by anisotropic etching in Process 3. However, the hard mask 114 is formed of such material as SiO₂ and SiON, so that it is difficult to reduce the mask size 210 by a gate etching step used in Process 3.

[0062] However, in the etching processing method according to the present embodiment, the mask size 210 is preliminarily acquired, and at least one parameter (variable parameter) in the recipe used is adjusted so that the result of etching will coincide with a target value, in Process 3; therefore, a desired gate length 211 can be obtained. Further, the processing can be performed without damaging the gate insulation film 112.

[0063] Even if the processing can be performed with the mask size 210 of the hard mask 114 constant each time of processing in the preceding Processes 1 and 2, the mask size may be varied due to disturbances such as secular change of the system in Process 3.

[0064] Even in such a case, according to the present embodiment, the variation amount of the gate length 211 due to the disturbances is preliminarily acquired, and the recipe to be used in Process 3 is adjusted based on the variation amount thus acquired, without any feedback to the preceding Processes 1 and 2, so that the desired gate length 211 can be obtained. Further, the processing can be performed without damaging the gate insulation film 112. In addition, in the case of performing a feedback to the preceding Process 1 or 2, a large-scale system is required. On the other hand, in the present embodiment, it is possible to cope with the problem by only Process 3, so that initial introduction burden (time, cost, etc.) of the production system can be alleviated.

[0065]FIG. 11 illustrates a method of using a film thickness monitor. Here, the case of controlling the gate length by adjusting the O₂ flow rate in the recipe is described as an example. FIG. 11A shows the process in the case where the flow rate of oxygen (O₂) is set to be O₂=X [ml/min], and FIG. 11B shows the process in the case where the flow rate of oxygen (O₂) is set to be O₂=X−a [ml/min].

[0066] In Step 1 of FIG. 11A, etching is performed for a predetermined time at an oxygen (O₂) flow rate of X ml/min. In this case, the residual film thickness (the film thickness to the gate insulation film as foundation) is Y. Next, in Step 2, etching is conducted until reaching the foundation. In the etching in Step 2, etching proceeds at an angle θ according to the recipe applied. Therefore, the final gate length is C1.

[0067] On the other hand, in the case of controlling the final gate length, etching is conducted at an oxygen (O₂) flow rate of X−a [ml/min] in Step 1, as shown in FIG. 11B. In this case, although the gate length can be controlled, the etching rate is also varied. As a result, the residual film thickness in Step 1 is Z (Z>Y). In the subsequent Step 2, the recipe is fixed, so that the etching proceeds in the same manner as in the case of FIG. 11A. That is, the etching proceeds at the predetermined angle θ. As a result, the final gate length is C2, which is different from the gate length C1 by C3 (this phenomenon can be utilized for controlling the CD value).

[0068] In other words, where it is intended to control the CD value by controlling the flow rate of oxygen (O₂) in Step 1 of FIG. 11B, the etching rate in Step 1 is varied. In this case, if the effect of modification of CD value in Step 2 is greater than the effect of modification of CD value due to modification of the oxygen (O₂) flow rate in Step 1, the control of the CD value by modification of the oxygen (O₂) flow rate in Step 1 is hidden, resulting in that an unexpected CD value is obtained.

[0069] Therefore, it is necessary to control the residual film thickness Y or the residual film thickness Z to a constantly fixed value. For this purpose, it is necessary to monitor the film thickness during the processing in Step 1 on a real-time basis.

[0070] While the polysilicon film has been taken as an example of the single film to be etched in the above description, the single film to be etched may be another film, for example, a laminate film with a metallic film.

[0071] According to the present invention, an etching system and method which can alleviate the fear of unexpected side effects, at the time of performing a feedback control, and can build up a control model without using enormous labor and time can be provided.

[0072] While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects. 

What is claimed is:
 1. An etching system for subjecting a single film to be etched to etching comprised of a plurality of etching steps applying respective different recipes, comprising: recipe generating means for fixing a recipe to be applied to the last etching step affecting an underlying film making contact with said film to be etched, of said etching steps, to a preset recipe, and generating recipes to be applied to the residual etching steps on the basis of processed results; wherein etching is conducted according to said recipes generated by said recipe generating means.
 2. An etching system for subjecting a single film to be etched to etching comprised of a plurality of etching steps applying respective different recipes, comprising: recipe generating means for fixings a recipe to be applied to the last etching step affecting an underlying film making contact with said film to be etched, of said etching steps, to a preset recipe, and generating recipes to be applied to the residual etching steps on the basis of a target value of processed results and a predicted value of processed results; wherein etching is conducted according to said recipes generated by said recipe generating means.
 3. An etching system as set forth in claim 2, further comprising a processed result estimating means for estimating results of etching on the basis of an output signal from a monitor for detecting the conditions of said etching system and an estimation model formed on the basis of the monitor output signal and results of etching.
 4. An etching system as set forth in any one of claims 1 to 3, wherein said recipe generating means updates at least one parameter during etching.
 5. An etching system as set forth in any one of claims 1 to 4, wherein said recipes generated by said recipe generating means are generated by modifying at least one of oxygen gas flow rate, etching time, high-frequency electric power supplied to a process chamber, and chlorine gas ratio (Cl2/(HBr+Cl2)).
 6. An etching system as set forth in any one of claims 1 to 5, wherein said single film to be etched is comprised of a laminate film.
 7. An etching system as set forth in claim 3, wherein said estimation model is generated on the basis of the correlation between a spectrum signal obtained by a plasma emission spectroscopic monitor for spectroscopically analyzing plasma emission in an etching process chamber and the results of etching.
 8. An etching system as set forth in any one of claims 1 to 7, further comprising a film thickness monitor for monitoring the residual film thickness of said film to be etched, wherein processing according to said recipes generated by said recipe generating means is finished on the basis of an output from said film thickness monitor.
 9. An etching method for subjecting a single film to be etched to an etching processing comprised of a plurality of etching steps applying respective different recipes, comprising the steps of: etching an upper layer portion of said film to be etched on the basis of an upper layer portion etching recipe generated by modifying at least one parameter in a fixed recipe preset on the basis of the results of the preceding processing; and etching a lower layer portion of said film to be etched making contact with an underlying film on the basis of said preset fixed recipe.
 10. An etching method for subjecting a single film to be etched to etching comprised of a plurality of etching steps applying respective different recipes, comprising the steps of: etching an upper layer portion of said film to be etched based on an upper layer portion etching recipe generated by modifying at least one parameter in a fixed recipe preset on the basis of the results of the preceding processing and a target value of processed results; and etching a lower layer portion of said film to be etched making contact with an underlying film on the basis of said preset fixed recipe.
 11. An etching method as set forth in any one of claims 9 and 10, wherein said results of processing are estimated on the basis of an estimation model formed on the basis of an output signal from a monitor for detecting the conditions of the etching system and the results of etching.
 12. An etching method as set forth in any one of claims 9 and 10, wherein a film thickness monitor for monitoring the residual film thickness of said film to be etched is provided, and said step of etching said upper layer portion of said film to be etched is finished on the basis of an output from said film thickness monitor. 